There is considerable interest in the design and fabrication of tandem multi junction solar cells for high efficiency photovoltaics for space-based and terrestrial applications. Multi junction solar cells comprise two or more p-n junction subcells with band gaps engineered to enable efficient collection of the broad solar spectrum. The subcell band gaps are controlled such that as the incident solar spectrum passes down through the multi junction solar cell it passes through subcells of sequentially decreasing band gap energy. Thus, the efficiency losses associated with single junction cells—inefficient collection of high-energy photons and failure to collect low-energy photons—are minimized.